Wet plugs on passenger side

[RichLo]

No need to replace injectors if your just having fuel pressure problems. But if you have the funds, I dont think it would hurt unless they QC failed ones. Spend extra and get AC Delco New or a quality re-manufactured pair. Also, be sure you cross reference the part numbers to make sure they dont give you 4.3, 305, or 454 injectors on accident.

 

[DougN2deep]

No need to replace injectors if your just having fuel pressure problems. But if you have the funds, I dont think it would hurt unless they QC failed ones. Spend extra and get AC Delco New or a quality re-manufactured pair. Also, be sure you cross reference the part numbers to make sure they dont give you 4.3, 305, or 454 injectors on accident.

I'm not sure if it's fuel pressure problems since it's only impacting the plugs on the passengers side. Doesn't seem to add up.

Wondering if the gasket is shot on the TBI perhaps, seems like if I'm in there it'd make sense to replace everything with the costs associated.

 

[DougN2deep]

Well swapped the fuel filter and couldn't do the fuel pressure test as I didn't have the right fitting.

Just test drove her and she idled better, had a more consistent acceleration and wouldn't back fire UNTIL about 5 minutes or 2 miles or so later! Then she went back to feeling real sluggish, misfiring or back firing, like bad gas or something.

Strange.

I've got a pump I could pull all the gas out of her with but just topped her off and my three 5 gallon spare tanks yesterday due to winter storm coming tonight ugh.

Is it worth hitting the neighbors up for some spare cans or is there a gas test I can run?

Other thought is there's an intermittent sensor as mentioned before picking up different readings.

 

[RichLo]

How many gallons were in it before you topped it off?

you could pour a few bottle of HEET gas line antifreeze in the tank and let it run for a few minutes to cycle it through. Could be some moisture in the gas.

 

[Schurkey]

I bought some bigger off road tires for her to grab wood in the mtns

That'll make the truck less peppy.

and some bigger front brakes/rotors (still need to install).

Define "bigger". You should already have the thicker rotors of the two kinds used on 1500s, and larger-diameter is going to be...interesting.

Took her out a few times in the last month and the acceleration has been boggy with some misfires/back fires.

Yeah, that's a genuine problem.

You still need to verify fuel pressure.
You're working on replacing the usual "tune-up" items.
And there's still the scan tool issue.

Pulled the plugs and all the passenger side plugs are wet w/oil.

The electrodes/porcelains of the plugs aren't "wet". Some have oil on the threads. One plug looks darker than the others, all of them have deposits probably from fuel. Start with fresh plugs and other "tune-up" items, see what happens. Assure that the ignition coil can throw a spark that will jump the gap of a spark-tester calibrated for HEI. I'd start with testing the coil wire pulled out of the distributor cap, and if that's good, move on to testing the plug wires at the spark plug end.

Wouldn't hurt to assure the PCV system isn't pulling oil due to faulty baffles in the valve covers, or a faulty PCV valve. Is the inside of the PCV valve hose wet with oil?

Did a compression test and all the cylinders are pretty even between 170-180 and one at 150.

Not optimum having one cylinder that much lower than the others, but not heartbreaking either. 150 should run just fine.

the TBI spray looks erratic and not like an umbrella.

Photo? Video?

Tried hooking up an OBD1 and no codes.

That's not good. Either the computer is screwed, your "OBD1" (whatever that is) is screwed, or the computer can't connect to the "OBD1" due to a wiring problem.

This is probably your first priority--get a REAL scan tool hooked-up and see if you have any codes beyond "12"; and especially look at the data stream. Verify EVERY sensor and computer output.

Have you checked the EGR system--hose routing, solenoid, EGR valve, and EGR passages for proper operation?

At some point you'll want to download the service manual set from the links in the sticky-thread section of this forum.

Both injectors look like they're not running steady. Lot of gas but not even.

They're not going to "run steady" at low speed--idle. They alternate firing left--right--left--right...etc.

you could pour a few bottle of HEET gas line antifreeze in the tank and let it run for a few minutes to cycle it through. Could be some moisture in the gas.

Or just buy gas with 10% Ethanol already mixed-in, from a gas station that doesn't have a reputation for leaky underground tanks (which is pretty-much all of them now--the EPA got involved in that decades ago.)

 

[Road Trip]

Pulled the plugs and all the passenger side plugs are wet w/oil. Did a compression test and all the cylinders are pretty even between 170-180 and one at 150. Replaced the plugs and no change. Pulled the air filter and the TBI spray looks erratic and not like an umbrella. Tried hooking up an OBD1 and no codes.

EDIT: ^^^ Reply collision -- 100% what Schurkey said above. ^^^

The following is just some additional troubleshooting info to keep in mind
when looking at spark plug coloring.

Greetings @DougN2deep,

I'd like to start by saying that your group photo of your spark plugs *with*
the associated compression test readings on the cardboard is excellent! Since
these 2 variables interact with each other, it gives a better than average overview
of what we've got to work with.

The only thing I'd change is to # the spark plugs per the Chevrolet convention. Here's
a photo of a TBI intake manifold with the Chevrolet numbering scheme overlaid:

You must be registered for see images attach

Note:
Cylinders fed by the passenger side throttle body injector (lower plenum) shown in RED.
Cylinders fed by the driver's side throttle body injector (upper plenum) shown in BLUE.

Pulling this all together from the troubleshooting perspective, IF I think that the driver's side Injector
is too rich or too lean and that's the root cause of the problem, then I would want to see the following
4 spark plugs to share the same wrong coloring: #2, #3, #5, and #8.

On the other hand, IF I think that the passenger side Injector is malfunctioning, then I would want to
see the following cylinders with the same wrong coloring: #1, #4, #6, and #7. Take a close look at your
photo and see if you can match either one of these failure patterns to what you have on display.

****

By the way, this intake manifold design is referred to as a 180° dual-plane. In English, it means that the
intake runners are organized and cast so that each consecutive cylinder filling is alternated between
the driver's side and passenger side throttles. Here's the firing order with the colors used above:

1 - 8 - 4 - 3 - 6 - 5 - 7 - 2

Neat trivia, sure. But I bring this up because with all the engine bay clutter over a typical intake manifold,
this intake feeding pattern isn't that easy to see. So for those newer to the engine hobby, I can see where
troubleshooting all the cylinders on the passenger side might be (erroneously) attributed to the passenger
side TBI Injector. (I'm not saying that all the passenger side cylinders can't look worse, A/F ratio-wise
than the driver's side, but in this case I would be taking a hard look at the handiwork of whoever was the
last mechanic to replace the intake manifold gasket. (!)

EDIT: Another way to see one side is better than the other is if at some point in the past only 1
cylinder head was replaced. (Think new valve stem guides/seals on 1 side, and the aged original stuff
on the other.) People sometimes do goofy things in order to save a buck?

****

Given that I can't discern a TBI Injector/Intake-related spark plug coloring, I would go with the previous
suggestions for replacing the spark plugs + wires + cap + rotor at a minimum, accumulate some miles
on the new plugs, and then pull *those* and post them so that we can all take a closer look at what you
have. (ie: put a good Schurkey on it, fix whatever you find, and then see what you've got.)

One last thing, if there's a discernible difference visually in the fuel delivery between the 2 TBI injectors,
then by all means do what it takes for them to match up.

Hope this helps. Best of luck getting your TBI GMT400 running like new again.

Cheers --

 

[DougN2deep]

EDIT: /\ Reply collision -- 100% what Schurkey said above. /\

The following is just some additional troubleshooting info to keep in mind
when looking at spark plug coloring.

Greetings @DougN2deep,

I'd like to start by saying that your group photo of your spark plugs *with*
the associated compression test readings on the cardboard is excellent! Since
these 2 variables interact with each other, it gives a better than average overview
of what we've got to work with.

The only thing I'd change is to # the spark plugs per the Chevrolet convention. Here's
a photo of a TBI intake manifold with the Chevrolet numbering scheme overlaid:

You must be registered for see images attach

Note:
Cylinders fed by the passenger side throttle body injector (lower plenum) shown in RED.
Cylinders fed by the driver's side throttle body injector (upper plenum) shown in BLUE.

Pulling this all together from the troubleshooting perspective, IF I think that the driver's side Injector
is too rich or too lean and that's the root cause of the problem, then I would want to see the following
4 spark plugs to have the wrong coloring: #2, #3, #5, and #8.

On the other hand, IF I think that the passenger side Injector is malfunctioning, then I would want to
see the following cylinders with the same wrong coloring: #1, #4, #6, and #7. Take a close look at your
photo and see if you can match either one of these failure patterns to what you have on display.

****

By the way, this intake manifold design is referred to as a 180° dual-plane. In English, it means that the
intake runners are organized and cast so that each consecutive cylinder filling is alternated between
the driver's side and passenger side throttles. Here's the firing order with the colors used above:

1 - 8 - 4 - 3 - 6 - 5 - 7 - 2

Neat trivia, sure. But I bring this up because with all the engine bay clutter over a typical intake manifold,
this intake feeding pattern isn't that easy to see. So for those newer to the engine hobby, I can see where
troubleshooting all the cylinders on the passenger side might be (erroneously) attributed to the passenger
side TBI Injector. (I'm not saying that all the passenger side cylinders can't look worse than the driver's side,
but in this case I would be taking a hard look at the handiwork of whoever was the last mechanic to replace
the intake manifold gasket. (!)

****

Given that I can't discern a TBI Injector/Intake-related spark plug coloring, I would go with the previous
suggestions for replacing the spark plugs + wires + cap + rotor at a minimum, accumulate some miles
on the new plugs, and then pull *those* and post them so that we can all take a closer look at what you
have. (ie: put a good Schurkey on it, fix whatever you find, and then see what you've got.)

One last thing, if there's a discernible difference visually in the fuel delivery between the 2 TBI injectors,
then by all means do what it takes for them to match up.

Hope this helps. Best of luck getting your TBI GMT400 running like new again.

Cheers --

Thank you.. That's a nice diagram gonna save that in my chevy folder.

This truck is growing on me (especially having a newer tundra with 3-4th starting to slip). The original owner kept good records and was a city inspector. Got her for $500 and put $700 into tires and $200 into a stereo and now maybe $100 for plugs,wires,cap/rotor,fuel filter. Grabbed a quart of paint to do the hood and roof in the summer and may grab a gallon and just do the whole truck. Really bring her back to life.

 

[Road Trip]

Thank you.. That's a nice diagram gonna save that in my chevy folder.

This truck is growing on me (especially having a newer tundra with 3-4th starting to slip). The original owner kept good records and was a city inspector. Got her for $500 and put $700 into tires and $200 into a stereo and now maybe $100 for plugs,wires,cap/rotor,fuel filter. Grabbed a quart of paint to do the hood and roof in the summer and may grab a gallon and just do the whole truck. Really bring her back to life.

BTW, Welcome to the GMT400 forum. These old trucks have a way of
giving more than they get, so I can understand how it can start to
grow on ya. It's happened to a bunch of us too. :0)

If it becomes a keeper, then consider starting a build thread so that
we can follow along. And don't be surprised if others start clamoring
for photos -- I think we learn a little bit from each one.

Enjoy your ride!

 

[DougN2deep]

Just got done putting in the new cap 'n rotor and spark plug wires as it started to snow.

Went and ran the same route, maybe 3 miles with quite a few quick stop 'n starts and she didn't even sputter or cough

Going to keep the fuel pressure regulator and gasket kit that's enroute and put it on after I get some miles down I think.

Since you guys are here is there anyway to get a bit more low end power without adding/investing in headers? I read removing the cat helps. I have a 18' fiberglass bass boat that I'd like to drop in at the local launch, but it's heavily silted and needs some muscle, also have a slide in camper I'll be camping with in the summer.

Appreciate everyone's help!

 

[Schurkey]

The only thing I'd change is to # the spark plugs per the Chevrolet convention.

I TOTALLY missed that. Thanks.

Just got done putting in the new cap 'n rotor and spark plug wires...

Went and ran the same route, maybe 3 miles with quite a few quick stop 'n starts and she didn't even sputter or cough

Good start. Keep going.

Since you guys are here is there anyway to get a bit more low end power without adding/investing in headers?

Thorough "tune-up", maybe another couple of degrees of initial spark advance, smaller-diameter tires or deeper gears.

I read removing the cat helps.

Only if the cat is defective--plugging/restrictive.

also have a slide in camper I'll be camping with in the summer.

Verify that your truck is suited to carrying a camper. GVWR, etc.

The distributor in your photo looks terrible. Get rid of all the loose rust, verify that the magnet isn't cracked.

You must be registered for see images attach

You must be registered for see images attach

You might as well remove the distributor to do this--looks like someone installed it a tooth or two off from where it should be. And of course the wires are numbered wrong as Road Trip mentioned already.